The need for effective and economical preservative compositions is well known. There are a wide variety of applications where inhibiting the growth of microorganisms is necessary, as for example personal care products such as shampoos, creams, lotions, cosmetics, and soaps and household products such as laundry detergents, hard surface cleaners, fabric softeners, and the like. The shelf life of these compositions depends on their resistance to microbial spoilage.
In addition, in many industrial compositions, antimicrobial agents are useful in paint, wood, textiles, adhesives, sealants, leather, rope, paper pulp, plastics, fuel, oil, and rubber and metal working fluids. The control of slime-producing bacteria and fungi in pulp and paper mills and in cooling towers is also a matter of substantial commercial importance.
Certain compounds have long been known to be useful as preservatives. Compounds such as the halopropynyl carbamates are known for their fungicidal activity; however, they are costly and, as a result, have only found applications in specialty areas where the high costs can be justified.
Other commercially known preservatives include Quaternium-15 (Dowicil 200, a trademark of Dow Chemical Company). It has the disadvantage of being a solid product which must be solubilized in water before it can be used in the end product. In aqueous solution it exhibits pH drift and causes formulation problems, particularly with regard to viscosity and color.
Formaldehyde in the free state, as in formalin, is effective only for short periods of time. In addition, it is inactivated by protein.
Alkyl parabens (e.g., methyl, ethyl, and propyl), which are useful as fungicides, have limited bactericidal action. They are generally solubilized in oil since they are poorly soluble in water, leading to formulation difficulties for personal care and household products. They are often inactivated by commonly used materials such as gelatin, methyl cellulose, and polyethylene glycol.
These preservatives have also included formaldehyde and isothiazolinone derivatives. U.S. Pat. No. 3,987,184 shows the use of 1,3-dimethylol-5,5-dimethylhydantoin (DMDMH) as a useful formaldehyde donor compound for the preservation of personal care products, cosmetics, and household and industrial products. Mixtures of 5-chloro-2-methyl-3-isothiazolin-4-one (CMI) and 2-methyl-3-isothiazolin-4-one (MI) have also been used to preserve personal care, household, and industrial products. While useful for controlling bacteria, fungi and other contamination in the products, these substances may be irritating and difficult to handle in the manufacture of end-use products such as shampoos.
More recently, less toxic substances have been used as preservatives, including iodopropynyl butylcarbamate, polyaminopropyl biguanide, bis(3-aminopropyl) dodecylamine, benzethonium chloride, methyldibromo glutaronitrile, and ethylene-diaminetetraacetic acid. However, to obtain full microbiological control, a greater amount of these preservatives must be added to the product, thereby making it more difficult to formulate. Also, when large amounts of additive are used, the likelihood of a negative impact on that product, such as instability, odor and breakdown of product, is greater. Moreover, some of these compounds, such as iodopropynyl butylcarbamate, are costly, so the use of large amounts of these compounds is not economical.
In light of the foregoing, it is clearly desirable to formulate a preservative which completely controls microbiological and fungal contamination in personal care products such as shampoos, conditioners and moisturizers, in household products with potential for contact with human skin and clothing, and in industrial products. The preservative should be easy to formulate and should be able to be used at levels low enough so as not to negatively impact the product. Also the preservative must be nontoxic and non-irritating at the levels used if it is to be used in personal care products, such as cosmetics and shampoos.